Plasma-enhanced processing has long been employed to process substrates into integrated circuit dies, which may then be further processed into integrated circuits for use in a variety of electronic devices. Plasma-enhanced processing includes, for example, plasma-enhanced etching, plasma-enhanced deposition, plasma-enhanced cleaning, and the like.
In the field of plasma-enhanced etching, a plasma is typically generated from etching feed gas that may include different constituent gases. The feed gas is energized by an energy source to form a plasma to etch the surface of a substrate. By using a variety of masks, different patterns may be created on various layers of the substrate. The plasma itself may be created using one or more plasma generation technologies, including for example, inductively coupled plasma, capacitively coupled plasma, microwave plasma, etc.
Commercial plasma chambers for etching dielectric wafer films are primarily based upon parallel-plate capacitively-coupled plasma (CCP). In this type of chamber, RF excitation at one or more RF frequencies is applied from one or more RF sources to one or more electrodes to generate an etching plasma from the provided etching source (feed) gas. The etching characteristics of the chamber are controlled through variations in numerous input parameters including, for example, pressure, choice of feed gas, flow rate for each feed gas, power for the RF sources, etc.
Even with these numerous control parameters, it is known that the chemical and physical characteristics of the plasma are interdependent and difficult to independently control. In other words, changing an input parameter (such as RF power or pressure) tends to result in changes in multiple plasma parameters and/or changes in multiple etch result parameters. The interdependencies among various plasma characteristics and/or various wafer etch results tend to be amplified in narrow-gap, capacitively coupled plasma processing chambers of the type employed in modern dielectric etch applications.
To elaborate, consider a simple example etch process based on CF4 feed gas only and a single RF excitation frequency. As RF power is increased, the degree of polymerization of the plasma-surface interaction will vary, typically increasing to a maximum and then decreasing. This behavior reflects the decomposition of CF4 at lower RF powers to form polymerizing radical species such as CF2. At higher RF powers, secondary decomposition of those radicals forms less polymerizing species such as C+F. This phenomenon provides some control of the degree of polymerization in the plasma using RF power settings.
However, a change in the input RF power also affects physical properties of the plasma, for example the plasma density, ion flux, and ion energy. This is because the control of chemical properties of the plasma, such as polymerization, is affected by the same parameters (such as RF power) that control the physical properties of the plasma (such as plasma density) such that the chemical and physical properties are strongly interdependent.
If the effects on the plasma characteristics can be decoupled when one or more input parameters are manipulated, more precise control of wafer etch result and a wider process window may be possible. For example, if the density of a specific polymerizing species can be controlled independently (i.e., in a decoupled manner) from the ion flux or electron temperature, more precise control of wafer etch result and a wider process window may be achieved.
Improving the decoupling of plasma characteristics and/or process etch results in order to optimize the etch to meet current and future etch specifications is one among many goals of the various embodiments of the present invention.